Adsorption of Monoazo Dyes (Crocein Orange G and Procion Red MX5B) from Water Using Raw and Acid-Treated Montmorillonite K10: Insight into Kinetics, Isotherm, and Thermodynamic Parameters

Waste water from textile and other industries containing dyes, especially azo dyes, are a serious health hazard. This study deals with removal of two least-studied anionic azo dyes, namely, Crocein orange G (COG) and Procion red MX5B (MX5B) from water with the help of montmorillonite and acid-treated montmorillonite. Structural changes of montmorillonite clay mineral after acid treatment were thoroughly investigated with the help of XRD, FTIR, SEM, BET surface area, and porosity measurements and zeta potential measurements. Influences of pH, interaction time, adsorbent amount, and temperature on adsorption were monitored, and the dye-clay mineral interactions were explained on the basis of physico-chemical characteristics of the materials. Acidic pH favored the adsorption of both dyes, and maximum adsorption was observed at pH 2.0 for both the dye. The dye-clay interaction reached equilibrium at 180min for COG and at 240min for MX5B, respectively. Adsorption kinetics and isotherm were studied in details, and it was observed that the adsorption process followed pseudo-second-order kinetics and Freundlich isotherm at 303K. Langmuir monolayer adsorption capacity for MX5B and COG were found to be 11.04 and 9.51mgg(-1), respectively, at 303K. Acid treatment of montmorillonite clay mineral showed 23.45 and 15.67% increase in adsorption capacity for MX5B and COG, respectively. The adsorption process is highly dependent on temperature and is endothermic in nature. This endothermic interaction is mainly driven by increase in entropy and decrease in Gibbs energy at higher temperature. This study successfully showed that montmorillonite and acid-treated forms can be effectively used to remove both COG and MX5B dyes from water.